1. Field of the Invention
The present invention relates to a plasma display panel and manufacturing method thereof, and more particularly, to a front substrate of a plasma display panel capable of concurrently forming a black layer placed within a discharge and a black matrix placed between discharge cells.
2. Background of the Prior Art
In general, plasma display panel (hereafter, referred to as PDP) is a display device using the visible rays generated when vacuum ultraviolet rays generated by gas discharge excite phosphor.
The PDP is thinner in thickness and lighter in weight than the cathode ray tubes (CRTs) that have been mainly employed as display devices. The PDP has an advantage in that a high definition and large-sized screen can be realized.
The PDP having such advantages described above includes many discharge cells arranged in matrix fashion, and each of the discharge cells forms one pixel of a screen.
FIGS. 1 and 2 show a structure of a general plasma display panel respectively. As shown in FIGS. 1 and 2, the plasma display panel includes a front substrate 10 on which an image is display and a rear substrate 20 spaced from the front substrate 10 with a predetermined interval and facing the front substrate 10. A plurality of sustain electrodes 11 are arranged in parallel on the front substrate 10. The sustain electrode 11 consists of a transparent electrode 11a and a bus electrode 11b. The transparent electrode 11a is made of ITO (Indium Tin Oxide) and the bus electrode 11b is made of conductive material such as silver. The bus electrode 11b is formed on the transparent electrode 11a. 
Generally, it is well known that silver (Ag) constituting the bus electrodes cannot transmit the light generated by discharge but reflects external lights. Such silver makes the plasma display worse in its contrast. To overcome this problem, a black electrode 11c is formed between the transparent electrode 11a and the bus electrode 11b to enhance contrast. A dielectric layer 12 limits discharge current and is coated on the sustain electrode 11. The dielectric layer 12 insulates a pair of the electrodes from each other. A protective layer 13 is formed on the dielectric layer 12 to make discharge condition better. Magnesium oxide (MgO) is deposited on the protective layer 13.
As shown in FIG. 2, a black matrix 14 is arranged between discharge cells. The black matrix 14 performs a light screening function to absorb external lights generated outside the front substrate 10 and reduce the reflection and a function to enhance the purity of the front substrate 10 and contrast. Stripe type (well type) barrier ribs 21 are arranged in parallel with each other on the rear substrate 20 to form a plurality of discharge spaces, e.g., discharge cells. A plurality of address electrodes 22 are arranged in parallel with the barrier rib and perform address discharge at the location where the address electrodes 22 cross over the sustain electrodes 11
RGB phosphorous layer 23 that is excited by the vacuum ultraviolet ray generated by a discharge cell and emits visible rays is coated inside the barrier rib 21. A lower dielectric 24 is formed on the rear substrate 20 and the entire surface of the address electrode 22 by annealing.
A method of manufacturing a front substrate of the conventional plasma display panel structured as above will be described.
FIGS. 3A through 3G show a method of manufacturing a front substrate of the conventional plasma display panel. As shown in FIGS. 3A through 3G, a transparent electrode 11a of ITO (Indium Tin Oxide) is formed on the front substrate 10. A black paste is printed on the front substrate 10 including the transparent electrode 11a and dried at a temperature of about 120° C. to form a black electrode layer as shown in FIG. 3A. Afterwards, a silver (Ag) paste is printed thereon and dried to form a bus electrode 11b as shown in FIG. 3B. The silver (Ag) paste is exposed to the ultraviolet ray using a first photomask 30 as shown in FIG. 3C. The exposed silver paste is developed and annealed in an annealing furnace (not shown in FIG. 3D) at a temperature of about 550° C. or higher for about three hours or more as shown in FIG. 3D. Thereafter, a dielectric paste is printed on the developed silver paste and dried as shown in FIG. 3E. Afterwards, a black matrix 14 is printed on a non-discharge area between discharge cells as shown in FIG. 3F. The dielectric layer and the black matrix are concurrently annealed in the annealing furnace (not shown in FIG. 3G) at a temperature of 550° C. or higher for about three hours or more as shown in FIG. 3G.
As described above, when manufacturing the front substrate of the conventional plasma display panel, the bus electrode 11b is formed by a total of three printing and drying processes that are performed once for each of black electrode layer 11c, bus electrode 11b and black matrix 14 and two annealing processes. To this end, the manufacturing process is too long and production costs are increased.
On the other hand, in general, it is desired that the interval between the bus electrodes in discharge cell is distant as possible as to enlarge the discharge space to improve the brightness. However, as the manufacturing method of FIG. 3, the bus electrode is formed only on the transparent electrode in the discharge cell, so that it is limited to enlarge the interval between the bus electrodes in the convention plasma display panel. If the bus electrode is formed on the non-discharge area, the silver (Ag) particle of the bus electrode migrates and bonds with the lead particle of the front substrate to change the color of the bus electrodes and lower the color temperature of the printed destination panel, which results in sudden reduction of brightness. In addition, silver particles of the bus electrode migrate to cause insulating destruction.
Accordingly, in the conventional plasma display panel, the bus electrode is formed on the transparent electrode in the discharge cell, so that improvement of the brightness depending on enlarging the interval between the bus electrodes is limited. Even though the bus electrode is formed on the non-discharge area with a predetermined interval, the silver (Ag) particle's migration changes the color of the bus electrode to lower the brightness.